1. Technical Field
The disclosure relates to a power transmission system provided in a vehicle and, more particularly, to a reduction of tooth hammer noise that occurs due to looseness in a power transmission path.
2. Description of Related Art
In looseness between rotary shafts that constitute a power transmission system provided in a vehicle, there is known that tooth hammer noise occurs as a result of a collision of teeth in the looseness, and measures for a reduction of the tooth hammer noise have been suggested. For example, in a power transmission system described in International Application Publication No. 2013/080311, a rotor shaft of a second electric motor constitutes part of a power transmission path from an engine to drive wheels. Therefore, the direct torque of the engine is transmitted to the rotor shaft. For this reason, even when the torque of the second electric motor is close to zero, the spline teeth of the rotor shaft are pressed against the spline teeth of the other rotary shaft while the engine is being driven. Thus, the looseness between the spline teeth of the rotor shaft and the spline teeth of the other rotary shaft is filled, and occurrence of tooth hammer noise is reduced.